Conventionally, there has been developed a classifier that determines the determination target such as a face of a pet such as a dog and a cat or a person included in the image. The classifier sets an area in the image as a search area, extracts a feature included in a display object in the search area, and determines that the determination target is present in the search area when the feature of the display object is matched with or similar to the feature of the determination target. FIGS. 13A and 13B schematically illustrate search areas RX and RX′ in the image. In FIGS. 13A and 13B, the dog face overlaps the search area RX. At this point, the classifier that sets the dog face to the determination target determines that the dog face is present in the search area RX. On the other hand, in FIG. 13A, the search area RX′ is out of the dog face. At this point, the classifier determines that the dog face is not present in the search area RX′.
For example, in a device disclosed in Japanese Unexamined Patent Publication No. 2005-115525, a configuration of a classifier group constructed with the plurality of classifiers is updated such that determination accuracy of a specific sample image is enhanced. More particularly, the device selects the classifiers having the high determination accuracy of the sample image from the plurality of classifiers, and combines the selected classifiers to produce the new classifier group. Japanese Unexamined Patent Publication Nos. 2008-204103, 2009-64162, 2010-9517, 2010-61415, 2010-170199, and 2011-138387 also disclose technologies for updating the configuration of the classifier.
However, sometimes the individual determination targets of the classifier have unique features different from each other. For example, in the dog face, a nose length, a patter, and a color depend on the type of dog. In such cases, unfortunately the classifier does not exactly determine the specific determination target, or hardly determines the specific determination target. For example, it is possible that the classifier that sets the dog face to the determination target determines the dog face having the short nose (see FIG. 13A) well but have difficulties determining the dog face having the long nose (see FIG. 13B).
In the device of Japanese Unexamined Patent Publication No. 2005-115525, the new classifier group is constructed by the combination of the plurality of classifiers such that the determination accuracy of the sample image is enhanced. However, the plurality of classifiers constituting the classifier group are produced by learning from the instance in which the sample image is not used. Accordingly, sometimes each of the classifiers has low determination accuracy of the sample image. In this case, the determination accuracy of the sample image can be insufficiently enhanced in the classifier group constructed with the classifiers. Additionally, Japanese Unexamined Patent Publication Nos. 2008-204103, 2009-64162, 2010-9517, 2010-61415, 2010-170199, and 2011-138387 do not disclose the technologies for sufficiently enhancing the determination accuracy of the specific determination target.